1. Field of the Invention
The present general inventive concept relates to an inkjet image forming apparatus, and more particularly, to a scanning type inkjet image forming apparatus which performs a printing operation with high resolution.
2. Description of the Related Art
A scanning type inkjet image forming apparatus forms an image by ejecting ink from a printhead that reciprocates in a direction that is perpendicular to a feeding direction of a print medium while being spaced apart from a top side of the printing medium by a predetermined gap. A printing quality is a very important factor in the scanning type inkjet image forming apparatus. Japanese Patent Laid-open Publication No. 2001-232781 describes a conventional inkjet image forming apparatus that enhances printing quality.
FIG. 1 illustrates ink dots ejected on a print medium P using the conventional inkjet image forming apparatus of Japanese Patent Laid-open Publication No. 2001-232781. FIG. 2 illustrates ink dots ejected on another print medium P using the conventional inkjet image forming apparatus. FIG. 3 illustrates ink dots ejected on another print medium P using the conventional inkjet image forming apparatus. In addition, FIG. 4 is an enlarged view of a portion of a print region of the printing mediums P of FIGS. 2 and 3.
A printhead 20 having a plurality of nozzles N1 to NN extending along a width of the print medium P in a direction that is perpendicular to a print medium-feeding direction (X-direction) is illustrated in FIG. 1. When the plurality of nozzles N1 to NN are sequentially driven, a deviation degree W that corresponds to a distance between a dot DD1 and a dot DDN is generated on the print medium P Here, the deviation degree W is a difference between positions of the dot DD1 ejected from a first nozzle N1 and the dot DDN ejected from an N-th nozzle NN. As the deviation degree W increases, ink is not ejected to a correct position and is ejected further from the other ink dots such that an image quality is lowered. The deviation degree W can be reduced using the following methods: as illustrated in FIG. 2, ink is ejected by dividing a plurality of head chips 21 into blocks so that each of the blocks is placed in a reverse order (i.e., alternating between a first direction and a second direction), or as illustrated in FIG. 3, ink is ejected by disposing the plurality of head chips 21 in a zigzag pattern so that each of the head chips 21 is placed in the reverse order. Thus, when time-division driving is performed in the reverse order, as illustrated in FIG. 4, the deviation degree W can be reduced. However, two ink dots are ejected to a predetermined region 10 and ink dots are not ejected to another region 30 so that a blank region that corresponds to the region 30 exists. Thus, a difference in optical density between the region 10 where ink dots are ejected to overlap and the region 30 where ink dots are not ejected occurs so that the image quality is lowered. This is a problem in the conventional inkjet image forming apparatus that attempts to print high quality images. Accordingly, an inkjet image forming apparatus having an improved structure becomes necessary.